Ah, yes that's right. Lol I'm taking ECMT1020 this semester
That's a good question. You can leave your semester 2 units until after you get your semester 1 marks back; that's perfectly fine.
Or you could select your semester 2 units right now, but for units where a prerequisite is needed, you can replace them with arbitrary units and then switch them out after you get your semester 1 marks back.